The present invention relates to a decorative material using a substantially transparent transfer sheet for giving an antistatic function to a surface of the decorative material, and also relates to a method for producing the same.
Heretofore, synthetic resin decorative sheets/plates are widely used as wall materials, ceiling materials, floor materials, furniture materials and so on because they have excellent surface characteristics.
There is however the fact that various troubles are caused by static electricity because this type of synthetic resin decorative sheets/plates have electrical insulating characteristics similar to those of general synthetic resins.
For example, troubles caused by static electricity, such as dusts and sparks which may be sometimes generated, in the processes of sheet/plate producing, secondary molding, coating, and the like, or in the final process in which this type of decorative sheets/plates are used by users, are too numerous to mention.
In recent years, clean rooms have been required strongly with the advance of precision in industry in the fields of electric/electronic techniques, communication appliances, medicines, foods and so on, so that measures of preventing static electricity have turned into a grave issue. To give electrical conductivity to a synthetic resin base, an application type method in which electrically conductive paint prepared by dispersing/dissolving electrically conductive powder and binder resin in an organic solvent to thereby form an electrically conductive film or a transfer type method in which an electrically conductive film is transferred to a base sheet after electrically conductive paint is preliminarily applied to a release film is employed conventionally. An electrically conductive matter is selected according to the purpose. That is, an electrically conductive matter such as a tin oxide, a indium oxide or the like is used as electrically conductive powder for the purpose of forming an electrically conductive film excellent in transparency (application type: Japanese Patent Postexamination Publication No. Sho-63-33779) (transfer type: Japanese Patent Unexamined Publication No. Sho-61-245866). On the other hand, an electrically conductive titanium oxide-coated matter such as a tin oxide (Japanese Patent Postexamination Publication No. Sho-63-33779), a zinc oxide (Japanese Patent Unexamined Publication No. Hei-1-153769 ), potassium titanate (Japanese Patent Unexamined Publication No. Hei-2-129265) or the like, is used for the purpose of forming a white or light electrically conductive film.
With respect to the former matter, electrically conductive oxides such as a tin oxide, an indium oxide and so on exhibit transparency by the superfine structure of electrically conductive powder. Because the electrically conductive powder per se is however dark gray, color change is remarkable in the case where the former matter is used in the decorative sheet. There arises a problem in that change in color, pattern and the like as a matter of life for the decorative sheet is large.
Furthermore, a film formed of this type fine powder has the property of turning the color to dark by light, though the cause is not clear. This is one reason why the film cannot be used in the decorative material.
On the other hand, with respect to the latter matter, a titanium oxide (the refractive index: 2.7), a zinc oxide (the refractive index: 1.9), a potassium titanate (the refractive index: 2.2) or the like reversely turns its color to white because the refractive index is different from that of the resin. Accordingly, the latter matter cannot be used in the decorative material.
Furthermore, in the aforementioned conventional structure, a problem arises in that fine cracks occur in the electrically conductive film when the synthetic resin plate having the electrically conductive film on its surface is thermally molded. This is because a mixture of electrically conductive powder suppresses the electrically conductive film from expanding sufficiently at the time of thermal molding.